The present invention relates generally to hot gas cleanup systems and more particularly to such systems that separate out, in addition to particulate matter, a molecular component of the gas.
Hot gas filtration systems are key components in advanced coal or biomass-based power plants. The hot gas filtration systems protect the downstream heat exchanger and gas turbine components from particle fouling and erosion, and clean the process gas to meet emission requirements. When hot gas filtration systems are installed in either pressurized fluid-bed combustion (PFBC), pressurized circulating fluidized-bed combustion (PCFBC), or integrated gasification combined cycle (IGCC) plants, lower downstream component costs are projected, in addition to improved efficiency, lower maintenance, and elimination of additional and expensive fuel and/or flue gas treatment systems. As a critical component, long term performance, durability and life of the porous ceramic and/or metal filter elements and associated high temperature, primary and secondary gasket seals are essential to the successful operation of hot gas filtration systems in advanced combustion and gasification applications. Utilization of this advanced barrier filter system concept extends as well to industrial applications where enhanced purity of product, separation of materials, and emissions control can be realized.
Examples of prior art hot gas filtration systems can be found in U.S. Pat. Nos. 5,433,771 and 5,876,471 assigned to the assignee of this application. The prior art teaches, as illustrated in FIG. 1, the use of a filter apparatus 20 for separating particulate matter from a gas stream. This apparatus includes a pressure vessel 22 in which there are mounted a plurality of clusters comprising a plurality of filter element arrays 26. These filter element arrays 26 include a plurality of xe2x80x9ccandle filter elementsxe2x80x9d 28.
The pressure vessel 22 has a dome shaped head 30 and body 32. The dome shaped head 30 terminates in a co-linear axial tubular extension 34 that defines an exit opening or nozzle 36 for the filtered gas to be removed from the vessel 22. The body 32 of the pressure vessel 22 includes an unfiltered gas inlet 25, an upper portion 38 that interfaces with the domed head 30, having a generally circular cylindrical shape, that is joined by a frusto-conical ash hopper 40 at the end opposite the domed head 30. The ash hopper 40, which is designed to receive the particulate matter, terminates at its opposite end in a linear coaxial extension that defines an opening or nozzle 42 that is connectable to an ash discharge line. A plurality of ports 44 extend from the dome shaped head 30. The ports 44 provide a site for inserting instrumentation and for viewing the interior of the domed shape head 30 during shutdown periods. Through each port 44 tubes 46 for supplying a back pulse burst of gas for cleaning the candle filters 28 can be placed.
Referring to FIG. 2, the pressure vessel 22 includes a tube sheet 48 which separates dirty and clean sides of the system, and which supports vertical clusters 27 best shown in FIG. 1. Each cluster 27 is comprised of one or more manifolds or plenums 29 which in turn supports arrays 26 containing filter elements 28, as best viewed in FIG. 2. Each plenum 29 comprises an upper plate 50 and a lower plate 52. In accordance with the present invention, each filter element 28 is held within a filter holder and gasket assembly 60 (best shown in FIG. 3) and coupled to the corresponding lower plate 52 of the plenum 29. Each cluster support pipe 58, as shown in FIG. 2, is supported parallel to the central axis of the pressure vessel 22. A dust shed or particle deflector 56 having a generally frusto-conical shape is attached above each plenum 29.
The prior art teaches the use of the filter holder and gasket assembly 60 as shown in FIG. 3 with a conventional thick-wall hollow tube monolithic ceramic. Fixturing for an alternate porous metal candle filter 28, and/or a thin wall composite and/or filament wound candle filter 28 is taught in U.S. Pat. Nos. 5,876,471, 5,944,859, 6,123,746 and 6,273,925. The filter holder and gasket assembly 60 provide a particulate barrier seal between the clean gas and dirty gas surfaces of the filter element 28. In FIG. 3, the filter holder and gasket assembly 60 for a conventional thick wall ceramic candle filter is shown assembled. The filter holder and gasket assembly 60 comprise a filter housing 62 having a peripheral sidewall 64 which defines an interior chamber 66, a fail-safe/regenerator device 68, permanently or removeably installed within the interior chamber 66, an annular spacer ring 70 permanently or removeably installed within the interior chamber 66, a gasket sock or sleeve 72, a top or topmost compliant gasket 74, a bottom or bottom-most compliant gasket 76 and a cast nut 78.
Preferably, the spacer ring 70 is permanently mounted to the fail-safe/regenerator to produce a single unit that is placed within the interior chamber 66 of the filter housing. In this case, the spacer ring 70 may be welded in abutment with the fail-safe/regenerator 68 to secure the fail-safe/regenerator 68 unit and to prevent the filter element 28 from moving and contacting the filter housing 62, thereby preventing possibly damage to the filter element 28. When the fail-safe/regenerator 68 is not incorporated into the filter housing 62, then only the spacer ring 70 will be securely mounted within the filter holder interior chamber 66. Alternately, the fail-safe/regenerator device 68 may be removeably mounted within the housing interior chamber 66 with the spacer ring 70 permanently mounted within the housing interior chamber 66. The fail-safe/regenerator device 68 is provided to prevent matter from travelling from the dirty gas stream to the clean gas area of the pressure vessel 22 if a candle filter element fails, is damaged or breaks. Additionally, the fail-safe/regenerator 68 will heat the back pulsed gas, which is generally cooler than the gas stream to prevent the filter element 28 from enduring thermal fatigue or cracking.
The fail-safe/regenerator unit 68, more fully described in U.S. Pat. No. 5,433,771, is a tubular metal unit 51 having perforated metal plates 53 welded to each end. Fine mesh screens 54, and heavy mesh support wires 55 are positioned adjacent to the metal plates 53 within the interior of the tubular member 51. The fine mesh screens 54 serve as the fail-safe mechanism to capture and retain fines, and plug in the event that a candle filter 28 fails, is damaged or breaks. The heavy mesh support wires 55 provide structure to support the fine mesh screens 54. Within the interior of the fail-safe/regenerator 68 raschig rings 73 are contained between the heavy mesh support wires 55, to heat incoming back pulsed gas that is used to clean the candle filters 28, which are part of the filter arrays 26 within the pressure vessel 20.
Applicants have found that in many hot gas filtering applications it is desirous to separate constituent components of the filtered gas such as in syngas applications. This can be achieved through the use of micro-porous membranes. A micro-porous membrane particularly suited to high temperature applications for separating hydrogen from a gas stream is particularly described in co-pending application Ser. No. 09/822,927 filed Mar. 30, 2001. Use of such membranes have been considered feasible in the temperature range of 600-1600xc2x0 F. (315-870xc2x0 C.). Hydrogen separation from syngas is a processing step having major market potential today in integrated refinery applications and for chemical synthesis. The high market potential of hydrogen production and the complementary aspects of producing a syngas concentrated in CO2 for removal and isolation, make the selection and implementation of hydrogen separation membranes as part of an integrated gas conditioning module, i.e., porous filter element (with or without catalytic enhancement) combined with a gas separation member unit, attractive.
Catalysts can be employed with the high temperature gas separation membrane to enhance the efficiency of the separation process. Catalytic reactors for syngas conversions of many types are commercially available and widely utilized in industry. The types of catalysts materials and operating temperatures needed are well known for example:
Tar cracking (Ni-based at 1200-1600xc2x0 F. (650-870xc2x0 C.))
Ammonia cracking (Ni-based at 1300-1600xc2x0 F. (705xc2x0 C.-870xc2x0 C.); RA-330(copyright) (available from Rolled Alloys, Temperance, Mich., USA) at 1200-1600xc2x0 F. (650-870xc2x0 C.); Zn-based at 900-1300xc2x0 F. (480-705xc2x0 C.))
COS hydrolysis (Ni-based at 900-1100xc2x0 F. (480-595xc2x0 C.))
Water-gas shift (Chromia-promoted iron oxide at 600-1500xc2x0 F. (315-815xc2x0 C.), CuOxe2x80x94Zn)xe2x80x94Al2O3, at 400-500xc2x0 F. (205-260xc2x0 C.).
Co-pending patent application Ser. No. 09/676,181, filed Sep. 29, 2000, teaches a method for catalytic enhancement of dual membrane filter elements. The foregoing patent application discusses the use of catalysts for reduction of NO, NH3, oxidation of methane, steam reforming and hydrogen treatment and SOx reduction. Incorporation of the catalyst directly onto or within the porous ceramic, continuous fiber ceramic composites (CFCC), metal, intermetallic, and/or metallic/ceramic composite filter body (i.e., wash coats of perovskite, zeolites, spinels, etc.; application via sol-gel; etc.), provides the basis for generation of specific catalytically-active porous media, i.e., filter elements, for use in advanced integrated gasification combined cycle coal-fired, oil-fired, and biomass applications. Similarly, the substrate Nickel-based materials, i.e., RA333(copyright) (available from Rolled Alloys, Temperance, Mich., USA), HR-160(copyright) (available from Haynes International of Kokomo, Ind., USA) and NiAl may act as a catalytic media that will not require the incorporation of additional catalytic enhancement species.
Accordingly, it is an object of this invention to combine the attributes of a hot gas cleanup filter with those of a hot gas separation membrane.
Additionally, it is a further object of this invention to combine the attributes of a hot gas cleanup filter and a gas separation membrane in a single module.
It is a further object of this invention to combine the attributes of the hot gas filter and gas separation membrane into a single module that replaces existing candle filters.
These and other objects are achieved in accordance with this invention by a hot gas cleanup system contained within a pressure vessel having a hot gas inlet and a first and second hot gas outlet. A primary chamber is formed within the pressure vessel in gas flow communication with the hot gas inlet. A secondary chamber is formed within the pressure vessel in gas flow communication with the first hot gas outlet. A candle filter assembly separates the primary chamber from the secondary chamber and a gas separation membrane is disposed within the secondary chamber; defining a third chamber in gas flow communication with the second hot gas outlet.
Preferably, the candle filter assembly includes a downstream regenerator and the gas separation membrane is disposed between the candle filter and the regenerator. In one embodiment, the candle filter is constructed from a porous metallic or intermetallic material and preferably the candle filter, gas separation membrane and regenerator are formed as an integral filtration unit. Desirably, the integral filtration unit is formed to fit in an existing candle filter housing to replace an existing candle filter.
In one advantageous embodiment, the gas separation membrane is formed as a tube having a first closed end and a second opened end that is affixed to and in gas communication with a gas conduit, which together with the interior of the gas separation membrane, comprises the third chamber. Preferably, the gas conduit extends through the regenerator.